Semi-flexible PCB technology

With simple depth-milling a standard printed circuit board can be prepared for flexible installations. So called "semi-flexible" printed circuits are offering a cost-efficient solution. They save connectors and increase reliability while decreasing size of the application and time needed for assembly. Semi-flexible PCBs are the perfect solution if you have flex-to-install requirements only and there is no dynamic bending during operation.

 

Often layout designers are reluctant to upgrade from a standard PCB with connectors to a notoriously expensive rigid-flexible printed circuit. The advantages are immense, but so are the costs and the layout requirements compared to standard PCBs. Many times this "jump" from standard technology to a high-tech segment is not necessary. Many printed circuits do not require dynamic bending capabilities in operation but only need to be fit into the housing neatly. This is called a "flex-to-install" requirement and here semi-flex offers a really cost-saving alternative technology.

 

 

Production of a semi-flexible PCB is identical with the manufacturing process of standard printed circuits. Semi-flexilbe boards can be produced as single-layer, double-layer or multilayer PCBs. With the exemption of a special solder mask that sustains bending, the materials are also identical to standard printed circuits. The only difference happens at the end of the production process when dedicated bending areas are milled down by z-axis routing. The remaining material can be bend and is thin enough to only carry the copper traces and little base material.

 

Design and installation of semi-flexible PCBs require some attention and modifications:

1.      The PCB should only be bend with copper on the outside of the bending area.

2.      Open copper structures, pads, annular rings or vias in the rigid part of the PCB should have a distance of at least 1mm from the bending area. In special cases 0,8mm are okay, too. The semi-flexible are cannot contain any vias, drills or open copper structures. The transition area from flexible to rigid should have a radius of 5mm or an obstuse angle. Trace-to-outline distance in the semi-flexible area should be minimum 0,30mm.

 

 

3.      The maximum bending radius depends on the lenght of the semi-flexible area:

 

4.      Currently, semi-flexible PCBs are possible up to 8 layers, while only one outer layer can be "semi-flexible" per bending area.

 

 

 

 

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JAAPSON, The Expert in HDI Multi-layer PCBs